sedimentary
Dendritic Agate (also known as Dendritic Siltstone or Mudstone)
Silicon Dioxide with Manganese/Iron Oxide inclusions (SiO2 + MnO2)
Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, or white base with black or dark brown tree-like patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, or white base with black or dark brown tree-like patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when mineral-rich water (carrying manganese or iron) seeps into cracks of existing sedimentary rocks or volcanic silica deposits. The water evaporates, leaving behind branching 'dendrite' crystals. They can range from millions to hundreds of millions of years old.
Uses & applications
Commonly used as a decorative lapidary stone, in jewelry (pendants, cabochons), and as a collector's specimen due to its unique 'landscape' patterns.
Geological facts
The word 'dendrite' comes from the Greek word 'dendron,' meaning tree. Despite looking like fossils, these patterns are purely inorganic mineral growths and are considered 'pseudofossils.'
Field identification & locations
Identify in the field by looking for fine, moss-like or tree-branch patterns on the surface of fine-grained stones. Common in arid regions or riverbeds in the Western US, Brazil, and India. It will not scratch with a pocket knife.
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